What could cause pain on the left back?

Causes of Left Back Pain

Pain on the left side of the back can be caused by a variety of conditions ranging from common musculoskeletal issues to serious systemic diseases that require prompt medical attention. 1

Common Causes of Left-Sided Back Pain

Musculoskeletal Causes

• Nonspecific back pain: Most cases (>85%) of back pain, including left-sided pain, are nonspecific and cannot be attributed to a specific disease or spinal abnormality 1
• Muscle strain or spasm: Particularly in the quadratus lumborum (most commonly involved), lower rectus abdominis, iliopsoas, and gluteal muscles 2, 3
• Myofascial pain syndrome: Trigger points in gluteal, pelvic, and lower extremity muscles can refer pain to the left back region 2
• Thoracic disc disease: Though less common than cervical or lumbar disc issues, thoracic disc herniations occur most frequently below T7 level 1

Spinal Pathology

• Radiculopathy: Compression of nerve roots causing radiating pain, particularly if pain follows a dermatomal pattern down the left leg 1
• Spinal stenosis: Narrowing of the spinal canal causing neurogenic claudication or pseudoclaudication 1
• Vertebral compression fracture: Common in the thoracic spine, especially in patients with osteoporosis, older age (>65), or chronic steroid use 1
• Left thoracic scoliosis: Though less common than right-sided curves, left thoracic scoliosis may be associated with underlying pathology, particularly in females 4

Serious Underlying Conditions

• Malignancy: Risk factors include history of cancer (LR 14.7), unexplained weight loss (LR 2.7), failure to improve after 1 month (LR 3.0), and age >50 years (LR 2.7) 1
• Infection: Discitis, osteomyelitis, or epidural abscess, especially in patients with risk factors like diabetes, IV drug use, immunosuppression, or recent infection 1
• Ankylosing spondylitis: Consider in younger patients with morning stiffness, improvement with exercise, alternating buttock pain, and night awakening 1

Non-Spinal Causes

• Visceral referred pain:
  • Renal: Kidney stones or pyelonephritis
  • Gastrointestinal: Pancreatitis
  • Vascular: Aortic aneurysm
  • Pulmonary: Pleural or lung pathology 1

Diagnostic Approach

Red Flags Requiring Urgent Evaluation

• Progressive or severe neurologic deficits (motor deficits at multiple levels)
• Bladder or bowel dysfunction (especially urinary retention - 90% sensitive for cauda equina syndrome)
• Fever with back pain (possible infection)
• History of cancer with new back pain
• Unexplained weight loss
• Severe, unremitting pain, especially at night
• Recent trauma in patients with osteoporosis risk factors 1

Physical Examination Findings to Note

• Location and radiation of pain
• Neurological deficits corresponding to specific nerve roots:
  • L4: Knee strength and reflexes
  • L5: Great toe and foot dorsiflexion strength
  • S1: Foot plantarflexion and ankle reflexes 1
• Straight-leg-raise test: Positive between 30-70° (sensitive but not specific for disc herniation)
• Crossed straight-leg-raise test: More specific (88%) but less sensitive (29%) 1

Imaging Recommendations

• No imaging is typically needed for acute (<4 weeks) uncomplicated back pain without red flags 1
• Consider imaging after 4-6 weeks of failed conservative treatment 1
• Early imaging warranted for:
  • Suspected cancer, infection, or cauda equina syndrome
  • Progressive neurologic deficits
  • Suspected vertebral compression fracture in high-risk patients 1

Treatment Approach

Treatment depends on the underlying cause but may include:

1. For nonspecific back pain: Conservative management with activity modification, physical therapy, and appropriate analgesics
2. For neuropathic pain components: Consider medications like pregabalin, duloxetine, or amitriptyline 5
3. For specific diagnoses: Targeted treatment based on the underlying cause

Important Considerations

• The thoracic spine is a common site for inflammatory, neoplastic, metabolic, infectious, and degenerative conditions 1
• Left-sided thoracic curves may have a higher association with underlying pathology than right-sided curves, particularly in females 4
• Always consider non-spine causes of back pain when the clinical picture is atypical 1

Remember that accurate localization of spinal levels is critical for diagnosis and treatment, as wrong-level identification occurs in 0.32% to 15% of cases 6.